The present invention relates to sewage settling tanks and in particular to a tank which employs tube settlers to increase the settling rate and a floating siphon system to improve the removal of sludge from the bottom of the settling tank.
Sewage settling tanks are well-known in the art and it is sufficient for the present merely to say that in such a tank the solids are allowed to settle to the bottom of the tank with the tank having some sort of weir arrangement to remove clarified water. It is known that the operation of settling tanks can be enhanced by employing tube settlers as described, for example, in U.S. Pat. No. 3,768,648. Where tube settlers are used it is common practice to provide a chain and flight system for removing the settled solids from the bottom of the settling tank beneath the tube settlers. In this respect, the chain and flight system uses a series of drive and idler pulleys which direct the continuous chain down into the settling tank and beneath the tube settler.
It is also known in the art to use a floating siphon system for removing sludge from the bottom of the settling tank. Such a system is illustrated for example, in my U.S. Pat. No. 3,333,704 and reference can be made to the patent for the details regarding the construction and operation of such a floating siphon system.
Heretofore, a floating siphon system for removing sludge from the bottom of the tank has not been compatible with tube settlers. This incompatibility arises because the area immediately above the tube settlers must be maintained as a clear water zone which is isolated from the other liquid in the settling tank. This isolation is accomplished by providing a baffle arrangement which upstands from about the periphery of the tube settlers to a point above the level of liquid in the settling tank. The floating siphon, on the other hand, must be free to move the whole length of the settling tank in order to permit the siphon inlet to sweep the area directly beneath the tube settlers. Accordingly, to provide the baffle arrangement with an opening to allow the floating siphon carriage to pass into and out of the water zone would likewise permit the passage of untreated water into the clear water zone.
The present invention, however, does permit the use of a floating siphon system in combination with a tube settler in a sewage settling tank while at the same time preventing the flow of untreated liquid directly into the clear water zone.